THE BIOLOGY BOOK

Regeneration

Stories of regeneration can be traced to Greek mythology. As punishment for the theft of fire, Zeus sentences Prometheus to be bound to a rock, where each day, an eagle feeds on his liver; the liver grows back, and the daily feedings continue. Another, the second of the Twelve Labors of Hercules, involves slaying the Lernaean hydra—each time a head is decapitated, it is replaced with two more. Less dramatic reports of regenerating lizard tails appear in the writings of ancient Greek scientists, including Aristotle.

Until the eighteenth century, biologists were largely content with observing and cataloguing the natural world. The Swiss naturalist Abraham Trembley was likely the first experimental biologist to manipulate living organisms and observe the consequences. While serving as a tutor for the children of a distinguished Dutch family, Trembley discovered polyps (Chlorohydra viridissima) in a fresh water pond. He found them intriguing when observing that the number of arms on individual organisms varied in number. When he cut the polyp in half, it regenerated into two fully complete individuals, and when cut into multiple pieces, multiple individuals materialized. After creating a seven-headed polyp, he called it a hydra, after the Greek mythological creature. In other experiments, he grafted two individuals together and a fused, single individual resulted. He detailed these experiments and his findings in a 1744 book. Trembley initially believed that polyps were plants, but seeing their movement caused him to revise this assessment. When he first found these strange creatures, Trembley was unaware of their earlier description by Antonie van Leeuwenhoek in 1702–1703, as one of his “animalculum.”

Although Trembley’s findings were lauded by much of the scientific community, they were not universally embraced. The ability of the dissected hydra to be regenerated into a complete replica of the original organism was contrary to the prevailing precept of preformation, that is, the embryo develops from pre-existing parts. Among the early doubters was Trembley’s cousin Charles Bonnet, he, too, a Swiss naturalist. But, Bonnet became convinced in 1745, when he observed similar regeneration in worms.